Elevated CO₂ and O₃ modify N turnover rates, but not N₂O emissions in a soybean agroecosystem

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• 作者：Charlotte Decock^a ; ^{cldecock@ucdavis.edu} ; Haegeun Chung^b ; Rodney Venterea^c ; Sharon B. Gray^d ; Andrew D.B. Leakey^d ; Johan Six^a
• 关键词：Natural abundance stable isotopes ; Nitrous oxide ; Climate change ; Greenhouse gases ; N-budget ; Agroecosystem ; Soybean
• 刊名：Soil Biology & Biochemistry
• 出版年：2012
• 期刊代码：96_00380717
• 类别：abs
• 出版时间：August, 2012
• 卷：51
• 期：Complete
• 页码：104-114
• 文件大小：752 K

摘要

In order to predict and mitigate future climate change, it is essential to understand plant-mediated effects of elevated CO₂ (eCO₂) and O₃ (eO₃) on N-cycling, including N₂O emissions. This is of particular interest for agroecosystems, since N-cycling and N₂O emissions are responsive to adaptive management. We investigated the interaction of soil moisture content with eCO₂ and eO₃ on potential N₂O emissions from SoyFACE during a 28-day laboratory incubation experiment. We also assessed field N₂O fluxes during 2 soybean-growing seasons. In addition, we sought to link previously observed changes in soybean growth and production to belowground processes over a longer time scale by analyzing changes in natural abundance stable isotope ratios of soil N (未¹⁵N). This method relies on the concept that soil 未¹⁵N can only change when inputs or outputs with an isotope signature different from that of soil N are altered. We found no major effects of eCO₂ and eO₃ on laboratory and field measured N₂O emissions. Natural abundance isotope analyses suggested, however, a decrease in belowground allocation of biologically fixed N in combination with decreased total gaseous N loss by eCO₂, resulting in a tighter N cycle in the longer-term. In contrast, the isotope data suggested an increase in belowground allocation of biologically fixed N under eO₃, leading to increased gaseous N loss, most likely in the form of N₂. Given that effects of eCO₂ and eO₃ on N pools and instantaneous transformation rates in surface soil layers of this agroecosystem have been minimal, our results illustrate the importance of evaluating longer-term changes in N turnover rates. We conclude that eCO₂ decelerates whereas eO₃ accelerates N-cycling in the longer-term, but feedback through changed N₂O emissions is not occurring in this soybean system.